Gadget Freak Case #232: Finding the Right Hydraulic Force

Ed Nauman found that using a hydraulic press to straighten a piece of material involved guesswork. You apply the force and then gradually increase it with each successive try. You usually track the appropriate force by counting the number of pulls on the pump handle. That's not very scientific.

Nauman created a gadget that indicates the actual force being applied. The goal was to make the process of using the hydraulic press quicker and more accurate.

I am with you Myron. In my years in the shop I straightened dozens of shafts, just as you describe. You put a block under the shaft/plate or whatever, at each end of the distortion, bent side up, and then apply pressure until it overbends. Measure with a straight edge and dial indicator, aplly that lesson and try again If there is a formula for how much over bend is required I have never seen it. This is also a problem I run into quite often in pressforming shallow bends. It may take many tries before you get to the right point of elastic deformation and it stays where you want it to be.

This device would have to be recalibrated everytime one of the points of contact has been changed. I can see where it would be usefull on a repetative operation (same shaft/same offset), but for just general arbor press bending, I think it would be a toy that would end up in a corner somewhere while work was being done.

If the only object is to straighten a piece of metal, then shouldn't we just apply enough force to "overbend" the workpiece to allow for springback and then measure the piece for straightness? Then, if necessary, hit the piece again and re-measure as necessary. It seems we just need a press with sufficient force to bend the metal.

I had the damaged journals of of a race-engine crankshaft welded and the rebuild shop did just as I described above to straighten the shaft before machining and grinding the journals. The press operation was done by "eyeball",and precision measurements were made with a dial indicator to check concentricity. That crank lasted several seasons with many sprints up to 9.000 rpm with no problems. Unless there is more to this story, I'm not sure why a force gauge is required.

The comment about the number of pumps on the handle was editorial and has nothing to do with the calibration or operation of this system. I was trying to relate how one goes about straightening something on a press that has no force indication or pressure gage. In which case, the only way to crudely estimate the force applied between successive 'trys' is to count the pulls on the handle.

I made the front panel. I used BobArt (from BobCAD) to generate the engraving artwork. I have a 10x54 3 axis CNC vertical mill in my garage that I used to cut the panel and engrave it. I also use the mill to make my own Printed Circuit Bords.

In case you missed it: "We have 38 hydraulic cylinders. We want to avoid running hydraulic piping to each of them, because that would be heavy, so we have electrovalves embedded in the wing to actuate the hydraulics. But if you had two wires, positive and negative, running to each electrovalve, your wing would look like a PG&E substation, and that's heavy too, so we use a CAN-bus [controlled area network] with far fewer wires. Still, it's incredibly complex.

"We wind up with lot of hydraulics," Cayard says, "and the America's Cup rules don't allow stored power, so two of our eleven guys—we think, two—will be grinding a primary winch all the race long. Not to trim, but to maintain pressure in the hydraulic tank so that any time someone wants to open a hydraulic valve to trim the wing, there will be pressure to make that happen."

The one I built has a pressure gauge like the one shown. The pressure on the gauge directly correlates to the pressure applied to the component being bent/mangled/distressed. The gauge displays psig which can be fairly easily converted to lbs of force. If I was developing a process and had to train someone else to use this device, I think this display would be much more useful. Good idea.

I needed a set of jacks made with pressure gauges like this once. We used them to check the compression force of springs on packaging equipment in several plants. We planned on calibrating them so we knew the force/PSI reading, and then using a table. But a little work by our supplier let us select a hydraulic jack that had a cylinder area close enough to 1" that we could just take the gauge reading in PSI and read it as lbs force. We confirmed it with a force gauge in the shop, and it was bang on.

In the "old days" a pressure gauge was used, located similarly to the pressure transmitter in this application. On some rams, the gauges were calibrated in lbs (or Tons), rather than psig, or sometimes both. I don't recall ever seeing one with a settable pointer, but that would be an obvious useful feature.

This is cool. I built my own 50-ton shop press using old fork-lift rails and would love to have this gadget.

However - Seems like there's some confusion here over relatively simple concepts. Such as equating the number of pumps on the handle to force? Doesn't the number of pumps equate to the volume of oil going into the ram which would equate to distance of ram travel? I would have simply gone to Excel; created a nice laminated graph correlating pressure to force and taped it to the press.

Adding a device to precisely measure the travel distance of the ram could be useful.

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